Copolymerizable fluorinated compounds, a process for their preparation and thermoplastic fluoropolymers obtainable therefrom

ABSTRACT

A 2-allyl-perfluoroalkyl-trifluorovinyl ether of the formula ##STR1## wherein R 1   F  and R 2   F  represent either --CF 3  or, together, (CF 2 ) n  where n=2 or 3, 
     is produced by 
     a) reacting hexafluoropropene oxide with a 2-allyl-substituted perfluorocycloketone or perfluoroketone, 
     b) subjecting the resulting 2-(allylperfluorocycloalkoxy)- or 2-(allylperfluyoro-alkoxy)-perfluoropropanoic acid fluoride to alkaline saponification thereby to form the corresponding sodium salt, 
     c) and decarboxylating the sodium salt at about 150°-350° C. 
     Polymers thereof produce amorphous, transparent coatings or molded items with glass transition temperatures between 60° and 150° C. and have good solubility characteristics in a number of organic solvents.

This application is a divisional of application Ser. No. 08/160,991,filed Dec. 2, 1993, which is a division of Ser. No. 08/075,207, filedJun. 10, 1993, now issued to U.S. Pat. No. 5,313,003, on May 17, 1994.

The present invention relates to2-allyl-perfluoro-(cyclo)alkyl-trifluorovinyl ethers, a process fortheir preparation and homo- and copolymers prepared therefrom.

The monomers according to the invention may be polymerized by radicalpolymerization with the formation of ring structures in the polymerchain (cyclopolymerization).

The polymers produce amorphous, transparent coatings or molded itemswith glass transition temperatures between 60° and 150° C. and have goodsolubility characteristics in a number of organic solvents. The latterhas proven to be particularly advantageous in that application onto asurface to be coated is just as easy as is subsequent dissolution, sothat the ability to recycle materials coated with the fluoropolymersaccording to the invention is increased.

When coating other polymeric materials, e.g. in the form of opticalfibers, with fluoropolymers, there is frequently the problem that, dueto the lack of solubility and relatively high fusion or softeningtemperature of fluoropolymers, application has to take place at too higha temperature for the material concerned, so that as a rule thermalstability and/or heat resistance are lost under the extreme conditions.

Amorphous, highly transparent fluoropolymers with cyclicchain-structural elements are known, e.g. from U.S. Pat. No. 4,975,505.However, these polymers have too high a glass transition temperature, atleast 150° C., for many applications and, furthermore, satisfactorysolubility characteristics am only demonstrated in selected fluorinatedcompounds.

EP-A 303,292 describes amorphous fluoropolymers which may be obtained bycyclopolymerization, which merely have glass transition temperatures ofless than 100° C. and which are likewise not soluble in common organicsolvents.

The present invention provides 2-allyl-perfluoroalkyl trifluorovinylethers of the following formula (I) ##STR2## wherein R¹ _(F) and R² _(F)represent either --CF₃ or, together, (CF₂)_(n) where n=2 or 3.

Monomers of the formula (I) where n=3 are preferred.

During radical polymerization, chain structures with the followingstructural units are produced: ##STR3##

Degrees of polymerization are achieved, depending on the temperature ofpolymerization, which correspond to a residual content of C--C doublebonds of less than 10% to 2% of the number of double bonds in themonomer.

The process according to the invention for preparing the monomersaccording to the invention is characterized in that

a) appropriate 2-allyl-substituted perfluorocycloketones orperfluoroketones are reacted with hexafluoropropene oxide,

b) the 2-(allylperfluorocycloalkoxy)- or2-(allylperfluoroalkoxy)-perfluoropropanoic acid fluorides obtained areconverted into their sodium salts by alkaline saponification and

c) the sodium salts are decarboxylated at 150°-350° C.

To reduce the production of2-allyl-perfluoroalkyl-1,1,1,2-tetrafluoroethyl ethers as a sideproduct, the sodium salts obtained under b) are preferably dissolved inaromatic hydrocarbons, insoluble salts are separated from the solutionand the sodium salts are dried azeotropically.

The 2-alkyl-substituted perfluorocycloketones or perfluoroketonesrequired to prepare the monomers according to the invention are knownper se; see e.g. Tetrahedron 23, 4243 (1967); U.S. Pat. No. 3,655,765.

However, it was extremely surprising that reaction of these startingcompounds with hexafluoropropene oxide is possible with satisfactoryyields, despite steric hindrance of the carbonyl group by the 2-allylsubstituents.

According to the invention, the reaction is performed in a suitablesolvent which contains a salt-forming agent, below room temperature,then the solvent is distilled off and the crude distillate isfractionated.

To convert the 2-allyl-substituted perfluorocycloalkoxy- orperfluoroalkoxy-perfluoropropanoic acid fluorides into2-allyl-substituted perfluorocycloalkyl trifluorovinyl orperfluoroalkyl-trifluorovinyl ethers according to the invention, thecarboxylic acid fluorides are converted into the sodium salts byalkaline saponification and these sodium salts are decarboxylated at150° to 350° C., preferably at 180° to 240° C.

Considerable amounts of 1,1,1,2-tetrafluoroethyl compounds are producedas a side product and these have to be separated with difficulty or atgreat expense.

For the compounds according to the invention, a process was found fordissolving the sodium salts initially formed in aromatic hydrocarbons,preferably toluene, separating out insoluble salts and drying the sodiumsalts azeotropically by distillation. In this way water and alkalineimpurities, which favor the appearance of the undesired1,1,1,2-tetrafluoroethyl compounds, are largely eliminated.

Thus, the 2-allyl-substituted perfluorocycloalkyl trifluorovinyl orperfluoroalkyl-trifluorovinyl ethers can be prepared with a high enoughpurity for polymerization trials.

Preparation of polymers according to the invention takes place via aradical route. In other respects, there are no restrictions on themethod of polymerization. Polymerization may take place in bulk,solution (suitable solvents are fluoro(hydro)carbons, e.g.hexafluoro-cyclopentane, perfluorobutane or fluorochlorocarbons; e.g.trichlorotrifluoroethane), suspension or emulsion. Radical initiationmay be promoted by energy-rich radiation, thermal energy or by radicalinitiators. Basically well-known compounds which are appropriate for theparticular reaction medium are used for chemical initiation.

Thus, organic, oil-soluble peroxides, which may also be fluorinated,such as benzoyl peroxide, trifluoroacetyl peroxide or organic, solubleazo-compounds, such as azobisisobutyronitrile, are used for bulk,solution and suspension polymerization. In the case of emulsionpolymerization, which is preferred for the preparation of copolymersaccording to the invention, water-soluble, inorganic per-compounds areused as initiators, such as persulphates, perborates, percarbonates;etc., generally in the form of their sodium or ammonium salts.

Depending on the polymerization temperature and on the decompositionconstant of the initiator, decomposition accelerators, generallyreducing agents, must also be used when using lower temperatures forpolymerization. The following may be used for this purpose: sulphurcompounds, such as sodium sulphite, sodium pyrosulphite or Rongalite C(sodium formamidinesulplfinic acid), other organic reducing agents, suchas ascorbic acid, metal salts, such as iron(II) or cobalt(II) salts,organometallic compounds, etc.

The reaction temperatures for copolymerization are between -15° and+120° C., preferably 0° to 90° C.

The following comonomers (II) may be considered for copolymerizationwith the monomers (I) according to the invention:

ethylene with at least one fluorine atom (vinyl fluoride, vinylidenefluoride, trifluoroethylene, tetrafluoroethylene,trifluorochloroethylene)

monomers of the CF₂ ═CYX type, wherein Y=H, F or Cl and X may representan aliphatic perfluorinated group (e.g. hexafluoropropene, hydro- orchloropentafluoropropene) or may be an R_(F) --O group (e.g.perfluoromethyl-perfluorovinyl ether;perfluorocyclopentyl-perfluorovinyl ether).

The copolymers may contain 1 to 99 mol % of the monomers (I) accordingto the invention, depending on the properties desired. The amount ofmonomer (I) should be at least 20 mol % if it is intended to becopolymerized to give an amorphous polymer with comonomers which mightform polymers which are capable of crystallizing.

Copolymerization with gaseous monomers is performed under elevatedpressure. This pressure should be at least 2 bar, but the value of 100bar need not be exceeded.

EXAMPLES Example 1

a) (2-Allyl-)heptafluorocyclopentanone

750 g (3.54 mol) of octafluorocyclopentene is initially introduced at 0°to 5° C. (ice bath), 205 g (3.59 mol) of KOH powder is added and thissuspension is stirred. Then 211 g (3.64 mol) of allyl alcohol is addeddropwise over the course of 3 hours, the small amount of exothermicenergy being trapped by the ice bath. Stirring is continued for 16 hoursat room temperature, then the mixture is stirred into 1500 ml of waterand the organic phase is separated and dried over Na₂ SO₄.

Crude yield; 785 g (3.14 mol)=88.7% of theory.

The crude material is subjected to distillation at atmospheric pressureusing a 30 cm Vigreux column with a destillation head. After removal ofthe volatile component (octafluorocyclopentene, ca. 32 g=0.151 mol) themixture is boiled under total reflux for 4 hours, until the sumptemperature has risen to ca. 140° C. (Rearrangement of the initiallyformed 1-allyloxyheptafluorocyclopentene to give(2-allyl-)heptafluoro-cyclopentanone; see Tetrahedron, 23, 4243 (1967);U.S. Pat. No. 3,655,765).

Actual distillation of the product now takes place

    ______________________________________                                        First runnings:                                                                           b.pt..sub.atm up 110° C. 67 g (GC; 63%)                                product, residual octafluoro-                                                 cyclopentene and                                                              a little allyl ether.                                             Main fraction:                                                                            b.pt..sub.atm 112° C. 615 g (2.46 mol = 69.4%)             Residues:   53 g                                                              ______________________________________                                    

b) 2-[2-(Allyl-)octafluorocyclopentoxy]perfluoropropanoic Acid Fluoride

150 g (2.59 mol) of ignited potassium fluoride are suspended in 500 mlof diglyme and 504 g (2.0 mol) of (2-allyl-)heptafluorocyclopentanoneare added dropwise over the course of 90 minutes, with stirring and at5° to 20° C. After the slightly exothermic reaction subsides, it iscooled to 5° C. and hexafluoropropene oxide is condensed in fast enoughfor only a slight reflux to occur in a dry ice condenser. After 330 g(ca. 1.99 mol) of hexafluoropropene oxide has been introduced (ca. 80 gper hour), stirring is continued overnight at room temperature.

Finally, the product and a proportion of the diglyme is distilled offunder a water jet vacuum up to b.pt.₁₈ mbar ca. 50° C. Crude weight 940g.

The coarse distillate is fractionated on a 30 cm packed column:

After a first running (102 g) of unconverted starting material, 554 g ofmain fraction (b.pt.₁₅ mbar 41° to 44° C.) are obtained which, accordingto GC, contains about 65% target product and ca. 30% diglyme.

Yield: 57.8% (with reference to the GC purity)

Ca. 15% target product, residual diglyme and multiple adducts of HFPOare left at the bottom.

¹ H-NMR: δ=2.83 ppm (dm,2H,--CH₂ --); 5.34 ppm (dm,2H,═CH₂) and 5.8 ppm(m,1H,CH═) (optional internal, TMS in CDCl₃).

c) 2-(Allyl-)octafluorocyclopentyl-trifluorovinyl Ether

554 g of distillate from Example 1b) [=ca. 360 g (1.02 mol) of2-[2(allyl)octafluorocyclopentoxy]-perfluoropropanoic acid fluoride] at0° to 5° C. are initially introduced into 300 ml of dioxane, andadjusted to be alkaline against phenolphthalein using 220 g of 45%strength sodium hydroxide solution over 3 hours. A suspension is formedwhich is concentrated to ca. 1/3 of its volume by evaporation under awater jet vacuum. The material is stirred up with 500 ml of toluene,then insoluble salts are removed by suction and washed with toluene.

The toluene solution is concentrated in a rotary evaporator, leavingbehind 553 g which is further concentrated under an oil pump vacuum at amaximum of 50° C.

The remaining 489 g of very viscous sodium salt are heated slowly to amaximum of 280° C., on a metal bath under an oil pump vacuum. Thematerial distilled off, via a bridge, at up to 100° C. bath temperature,consists to a large extent of residual toluene and diglyme and isdiscarded. From 150° to 180° C., thermal decomposition of the sodiumsalt starts. 352 g of distillate are collected, which are fractionatedon a 30 cm packed column under a water jet vacuum:

    ______________________________________                                        First runnings: b.pt..sub.18 mbar                                                             <35° C.; 45 g; rejected.                               Fraction I b.pt..sub.18 mbar                                                                  41-48° C., 189 g, GC shows 77%                                         target product, 15% diglyme                                   Fraction II b.pt..sub.18 mbar                                                                 >50° C., 57 g of largely diglyme                       Residue         ca. 50 g, crossed products.                                   Product fraction I is re-distilled on the same column:                        Fraction I b.pt..sub.18 mbar                                                                  45-47° C., 155 g, GC shows 88%                                         target product                                                Residue         ca. 30 g, <3% diglyme                                         ______________________________________                                    

¹ H-NMR: δ=2.79 ppm (dm,2H,--CH₂ --); 5.30 ppm (dm,2H,═CH₂) and 5.72 ppm(m,1H,CH═) (optional internal TMS in CDCl₃).

The 1,1,1,2-tetrafluoro-ethoxy compound occurring as an impurity givesan additional ¹ H resonance at 6.05 ppm.

Example 2

a) (2-Allyl-)pentafluorocyclobutanone

320 g (1.98 mol) of hexafluorocyclobutene are condensed into 116 g (2mol) of allyl alcohol at -5° C. Then, 113 g (1.98 mol) of KOH, dissolvedin 150 ml of water, are slowly added dropwise, over the course of 3hours, the temperature being kept at 0° to 5° C. Finally, stirring iscontinued overnight at room temperature.

The above is stirred into 1000 ml of water and the organic phase isseparated and dried over Na₂ SO₄.

Crude yield: 372 g.

The crude material is thermally rearranged, as described in Example 1a),and then fractionated at atmospheric pressure.

    ______________________________________                                        b.Pt..sub.atm                                                                         63-65° C., 289 g (95% from GC; 1.44 mol = 73%).                Residue 75 g.                                                                 ______________________________________                                    

b) 2-[2-(Allyl-)hexafluorocyclobutoxy]-perfluoropropanoic Acid Fluoride

1 mole of the ketone from Example 2a) is reacted with hexafluoropropeneoxide in the same way as in Example 1b).

After working up, a product fraction (b.pt.₁₈ 34°-36° C.) is obtained,which is ca. 85% (GC) target compound. The yield is ca. 60%.

c) 2-(Allyl)-hexafluorocyclobutyl-trifluorovinyl Ether

The carboxylic acid fluoride (0.5 mmol, 85%) from Example 2b) isconverted into a sodium salt in the stone way as in example 1c) andpyrolyzed at 150°-220° C. under an oil pump vacuum. The condensate isfractionated under a water jet vacuum.

Yield: 27% with reference to the carboxylic acid fluoride used.

b.pt.₂₀ mbar : 32°-33° C., GC shows 82% target product.

Example 3

a) (3-Allyl-)heptafluorobutan-2-one

396 g (1.98 mol) of octafluorobut-2-ene is condensed into 116 g (2 mol)of allyl alcohol at -5° C. Then 113 g (1.98 mol) of KOH, dissolved in150 ml of water, is slowly added dropwise over the course of 3 hours,the temperature being maintained at 0°-5° C. Stirring continuesovernight at room temperature and working-up is performed in the sameway as in Example 2a.

Crude yield 438 g.

The crude material is thermally rearranged in the same way as in Example1a) and then fractionated at atmospheric pressure.

b.pt._(atm) : 87°-89° C., 348 g (97% strength according to GC; 1.46mol=73.8%)

Residue: 85 g

b) 2[3-(Allyl-)heptafluorobut-2-oxy]perfluoropropanoic Acid Fluoride

1 mole of the ketone from Example 3a) is reacted with hexafluoropropeneoxide in the same way as in Example 1b).

After working-up, a product fraction (b.pt.₁₈ 56°-58° C.) is obtainedwhich is about 78% target compound (from GC); the yield is about 42%.

c) 3-(Allyl-)heptafluorobut-2-yl-trifluorovinyl Ether

The carboxylic acid fluoride (0.5 mol, 78% strength) from Example 3b) isconverted into the sodium salt in the same way as in Example 1c) , andpyrolyzed under an oil pump vacuum at 150°-230° C. The condensate isfractionated under a water jet vacuum.

Yield: 29% with reference to the carboxylic acid fluoride used.

Example 4

30 g of 1,1,2,2,3,3-hexafluorocyclopentane, 50 mg of diisopropylperoxydicarbonate and 15 g of 2-(allyl-)octafluorocyclopentyl-trifluorovinylether (with the purity described in Example 1) were placed in a 100 mlglass flask and cooled to -50° C. with stirring. The pressure in thereaction apparatus was reduced three times to about 4 mbar and flushedout with nitrogen each time. The reaction mixture was heated to 40° C.with constant stirring. After a total reaction time of 40 hours at 40°C., the mixture was cooled down. A viscous, colorless solution with asolids content of 31.4% by weight was obtained and precipitated bystirring into ethanol. 13 g of a white, powdery polymer were isolated.The polymer is soluble in acetone. The residual amount of unconvertedfluorovinyl groups, determined by ¹⁹ F-NMR spectroscopy, is less than 9mol %, with reference to the fluorovinyl groups used (evaluated usingthe signal at -115 ppm in acetone-d₆ against CFCl₃ as a standard). Inthe ¹ H-NMR spectrum the amount of unconverted allyl groups wasdetermined at less than 4 mol %, with reference to the allyl groups used(evaluated using the signal at 5.3-5.5 ppm: 2 doublets and at 5.9 ppm: 1sextet, measured in acetone-d₆).

[η]=0.031 dl/g (acetone/25° C.)

DSC: T_(g) =100° C.

Example 5

40 g of deionized water, 0.16 g of lithium perfluorooctylsulphonate, 0.3g of potassium peroxydisulphate and 10 g of2-allyl-octafluoro-cyclopentyl-trifluorovinyl ether (with the puritydescribed in Example 1) were placed in a 100 ml glass flask and cooledto 1° C. with stirring. The pressure in the reaction apparatus was thenreduced 5 times to about 20 mbar and flushed out with nitrogen eachtime. The reaction mixture was heated to 70° C. with constant stirring.After a total reaction time of 10 hours at 70° C., the mixture wascooled down. After standing for several hours, about 1 g of a viscous,oily phase settled out on the base of the reaction vessel, which wasseparated off. 4.5 g of a white powdery polymer were isolated from thesupernatant milky-white emulsion by coagulating with a 4% strengthaqueous magnesium sulphate solution. The polymer is soluble inbistrifluoromethylphenol (BTFMP) and acetone without forming a gel. Thelimiting viscosity number is 0.042 dl/g (THF/25° C.); DSC: T_(g) =64° C.

Example 6

Example 5 is repeated at 90° C. After a total reaction time of 4 hours,about 2 g of a viscous, oily phase settles out on the base of thereaction vessel, after cooling and standing for several hours. 3.5 g ofa white powdery polymer were isolated from the supernatant milky-whiteemulsion by coagulating with a 4% strength aqueous magnesium sulphatesolution. The polymer is soluble in bistrifluoromethylphenol (BTFMP) andacetone without forming a gel. The limiting viscosity number (Staudingerindex) is 3.5 ml/g (THF/25° C.). The weight average molecular weight,determined in THF by gel chromatography, is 1.3×10⁴ g/mol with anon-uniformity of 0.6 (polystyrene calibration curve).

DSC: T_(g) =58° C.

Examples 7-9

Copolymerisation of 2-allyl-octafluorocyclopentyl-trifluorovinyl etherwith trifluorochloroethylene 130 ml of deionized water were initiallyplaced in a 0.3 l autoclave. 0.5 g of lithium perfluorooctylsulphonatewere dissolved therein. This solution was adjusted to a pH of about 10using lithium hydroxide. Then nitrogen at a pressure of 10 bar wasadmitted to the sealed autoclave and the pressure was released toatmospheric pressure, three times in succession. The amounts given inTable 1 (=monomer 1) of 2-allyl-octafluorocyclopentyl-trifluorovinylether (as in Example 1) and 30 g of trifluorochloroethylene were placedin the autoclave and the reaction mixture was heated to 70° C. withstirring. After reaching this temperature, 20 g of an aqueous solutioncontaining 0.5 g of potassium peroxydisulphate were forced into theautoclave. After the total reaction times given in Table 1, the contentsof the autoclave were cooled and the unconverted mixture was evacuated.The reaction mixtures obtained in this way were poured into 130 ml of a4% strength aqueous magnesium sulphate solution to coagulate them fully.The products were washed with water and then dried, giving copolymers(white powders) consisting of units of trifluorochloroethylene and2-allyl-octafluorocyclopentyl-trifluorovinyl ether in the yields andcompositions (using the ¹⁹ F-NMR spectra or analysis of elementalchlorine), as given in Table 1.

Solubilities, limiting viscosity numbers [η] and DSC results are alsolisted in Table 1.

Furthermore, the polymer composition is given as the molar ratio of thepolymer structural units resulting from trifluorochloroethylene to thepolymer structural units resulting from2-allyl-octafluorocylcopentyl-trifluorovinyl ether.

(1) - means that complete dissolution was not achieved; + means that agel-free solution was obtained 25 mg of polymer per ml of acetone at 25°C. were used in each case.

                                      TABLE 1                                     __________________________________________________________________________                                      [η]                                                Time of polym.                                                                        Yield of                                                                            Comp. of polymer                                                                       [dl/g]   Tg form DSC                                                                          Solubility                  Example                                                                            Monomer 1                                                                           [hrs]   polymer [g]                                                                         (molar ratio)                                                                          (acetone 125° C.)                                                               [°C.]                                                                         (1)                         __________________________________________________________________________    7     7    10      16    90/10    0.065    60     -                           8    10    10      12    79/21    0.063    64     +                           9    20    20      27.5  67/33    0.052    72     +                           __________________________________________________________________________     (1)                                                                           - means that complete dissolution was not achieved                            + means that a gelfree solution was obtained 25 mg of polymer per ml of       acetone at 25° C. were used in each case                          

What is claimed is:
 1. A polymer or copolymer, containing at least oneof the monomeric structural units of the formula ##STR4## wherein R¹_(F), R² _(F) represent either --CF₃ or, together, (CF₂)_(n), where n=2or 3.